1. Field of the Invention
The invention relates to the use of polymers which contain, in copolymerized form, an α-olefin, a vinyl ester and an ester of an α,β-unsaturated carboxylic acid as an additive for fuel oils and lubricants and in particular as a cold flow improver in fuels; to the fuel oils and lubricants additized with these polymers; and to additive packages comprising such polymers.
2. Description of the Related Art
On temperature reduction, mineral oils comprising paraffinic waxes, such as middle distillates, diesel and heating oils, exhibit a distinct deterioration in the flow properties. The cause of this is the crystallization occurring from the cloud point temperature of relatively long-chain paraffins which form large, platelet-shaped wax crystals. These wax crystals have a spongelike structure and lead to inclusion of other fuel constituents in the crystal structure. The occurrence of these crystals leads rapidly to clogging of fuel filters both in tanks and in motor vehicles. At temperatures below the pour point (PP) the fuel eventually does not flow at all.
To alleviate these problems, fuel additives, which frequently consist of combinations of nucleators for early formation of very small crystals of the paraffins with the actual cold flow improvers (also known as CFI or MDFI), have already been added in small concentrations for some time. These in turn exhibit similar crystallization properties to the paraffins of the fuel, but prevent their growth, so that it is possible for it to pass through the filter at distinctly lower temperatures compared to the unadditized fuel. The cold filter plugging point (CFPP) is determined as a measure thereof. Further additives which can be used are wax antisettling additives (WASA), which prevent the settling of the very small crystals in the fuel.
Depending on the composition of the base fuel and of the additive, cold flow improvers are added in amounts of from about 50 to 500 ppm. The prior art discloses various CFI products (cf., for example, U.S. Pat. Nos. 3,038,479, 3,627,838 and 3,961,961, EP-A-0,261,957 or DE-A-31 41 507 and 25 15 805). Common CFIs are usually polymeric compounds, in particular ethylene-vinyl acetate (EVA) copolymers, for example the products sold by BASF AG under the tradename Keroflux.
Combinations of conventional CFIs with lubricity improvers (esters of mono- or polycarboxylic acids with mono- or polyalcohols) are also described as improved CFI combinations (EP-A-0 721 492).
EP 0922716 describes a process for preparing terpolymers which, in addition to ethylene, contain, in copolymerized form, at least two further ethylenically unsaturated compounds such as vinyl esters, acrylic or methacrylic esters, alkyl vinyl ethers or higher olefins. These are said to be suitable as flow point improvers of mineral oil distillates.
DE 1902925 describes terpolymers which contain, in copolymerized form, ethylene, vinyl esters of short-chain carboxylic acids, such as vinyl acetate, and long-chain unsaturated monoesters, such as vinyl esters of long-chain carboxylic acids, or acrylic esters which derive from long-chain alcohols. These are said to lower the pour point of middle distillates and improve their filterability.
U.S. Pat. No. 4,156,434 describes terpolymers which, in addition to ethylene and vinyl acetate, contain, in copolymerized form, an acrylic ester which derives from C12-C24-alcohols. These are said to lower the pour point of gas oils. No filterability-improving action is described.
There is a continuing need for further additives having CFI properties, especially those which are less expensive to use, for example because they improve the cold flow properties of fuel oils or lubricants and especially the filterability of fuel oils in lower dosage than commercial CFIs.